1. Field of the Invention
The present invention relates to an image data processing apparatus for processing image data, and outputting the processed image data.
2. Description of Related Art
An image reader for reading an original by fragmenting it into pixels has been conventionally used as an image input device for a digital copying machine or facsimile machine, an OCR (optical character reader), an optical filing system, and a variety of display devices which form, store, and display an image by a combination of pixels having a fixed size.
With this type of image reader, image information is quantized and handled as digital image data to carry out various image processing with ease. Generally, the image reader is constructed for image processing to improve image quality such as by emphasizing edges (contours) for clear definition of an image and smoothing for a natural image, and for image processing to enable image editing.
Known image editing operations include trimming for extracting only a particular area of an original, masking for blanking a particular area, reversing between negative and positive (black and white), and color conversion for changing a particular color portion into a different color.
U.S. Pat. No. 4,750,044, for example, discloses an image reader capable of image editing which includes an attribute memory for storing attribute data corresponding to the nature of image processing. Attribute data corresponding to small image areas into which an original is segmented are stored in the attribute memory in advance, and image processing based on the attribute data is carried out in real time in parallel with image reading.
With this image reader, types of image processing may be designated for the respective image areas to enable complicated and diverse image editing.
As is well known, to realize high quality reproduction images in the image processing of binary multivalue data corresponding to density levels of respective pixels in an original (hereinafter referred to as binarizing processing), simple binarizing processing in which the multivalue level of one pixel is compared with a fixed threshold level is suited for line images such as characters. Pseudo-tone processing based on the dither method or error diffusion method, on the other hand, is better suited for halftone images such as photographs.
It is therefore necessary, when reading an original having a mixture of line images and halftone images, to change the binary processing modes in accordance with attributes of the images indicating whether the images are line images or halftone images (hereinafter referred to as binary attributes).
There are image readers including a device for discriminating the binary attributes by various methods as disclosed in Japanese Patent Publication Kokai No. 62-39978 and other publications. The image readers capable of color editing such as color conversion include a device for discriminating color attributes of images.
Since conventional image readers output only image data after it has been processed, attribute data used for processing are not output. Accordingly, there is a problem when an operator or an external apparatus handling the image data received from the image reader does not recognize how the image data has been processed.